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THIS AVALANCHE ADVISORY EXPIRED ON January 3, 2018 @ 5:26 amAvalanche Advisory published on January 2, 2018 @ 5:26 am

Issued by
Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Heightened avalanche conditions exist at the upper elevations due to wind slabs from last weekends storm. At lower elevations multiple slab layers persist but are proving to be less reactive in stability tests. Stay safe by practicing safe travel habits as these more stubborn slabs can lull one into complacency by reinforcing bad habits and a false sense of security.

Kootenai

Heightened avalanche conditions exist at the upper elevations due to wind slabs from last weekends storm. At lower elevations multiple slab layers persist but are proving to be less reactive in stability tests. Stay safe by practicing safe travel habits as these more stubborn slabs can lull one into complacency by reinforcing bad habits and a false sense of security.

The storm that rolled in December 28th thru the 30th brought with it shifting winds at the upper elevations as it came and left us. This left pillows of wind slab on all aspects of the highest terrain above 6,000'. These slabs will likely be found just below ridgelines and in steep, cross-loaded gullies. Look for pillow like features in the snow surface and changes in surface density as you travel.

Avalanche Problem 2: Persistent Slab

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The storm snow from last weekend came in cold then transitioned to a relatively warm and dense snowfall as it dropped its last 6-10". This created a "upside down" slablayer (denser snow on top of lighter snow) at the top of our snowpack. This slablayer is very noticeable under foot and in many locations released naturally during or immediatly after the storm. There was widespread evidence of this layer releasing on all aspects and elevations yesterday. Now that this storm snow has had time to settle out and strengthen it is actually showing very little reactivity under foot and in stability testing. It is possible that you may see this top 6-10" move on steep, convex rolls resulting in small avalanches. The bigger concern is that a small avalanche from this recent storm snow will step down to a deeper weakness such as the facetlayer on the Thanksgiving rain crust, or a buried layer of surface hoar. Previous outings last week revealed that surface hoar was present and now likely buried at elevations below 6,000' on sheltered aspects. I could not find any yesterday; but, I would use caution in steep gullies near drainage bottoms and travel as if it is there till proven otherwise.

Yesterday we travelled into the Eastern Cabinets and performed stability tests at drainage bottom (4,500') and near the ridgeline at 6,000' on northerly aspects. On the climb in we observed extensive evidence of small, natural avalanches that released the top 6" of storm snow. The denser surface slab was also very evident under foot as one travelled you could feel the slab slightly supporting you before it broke under foot. Stability tests showed that this layer was failing with moderate force but not propagating across the column. I was also able to get on some smaller, convex terrain features and steep gullies where it would be most likely to fail and had was unable to make anything move or crack. The view from the ridgelines proved my assumption that battling winds indeed left multiple wind slabs on the higher terrain. The Thanksgiving rain crust and the slick layer of facets that are resting on it are now deeply buried in the Cabinet range and are not proving to be very reactive as we have a thick layer of cohesive snow overlying it. In the Purcell range the snow is not as deep and the facetlayer is thick with larger crystals. This thinner snowpack of the Purcell Ranges is likely to make this deep weak layer more sensitive to human triggers. It may take alot of force to trigger it such as cornice fall, warm temps or your buddy catching some sweet air off of a large cornice.

Weather and CURRENT CONDITIONS

weather summary

Backcountry Forecast from NWS Missoula issued:
420 AM MST Tue Jan 2 2018
DISCUSSION: Aside from the gusty winds along the Continental
Divide in the Glacier Park area this morning, light winds will be
common for much the Northern Rockies today. Sub zero air
continues hang around the Divide this morning as well, however
high clouds today are anticipated to start moderating high
elevation temperatures across the Northern Rockies through the end
of the week. Radiational cooling each overnight will continue to
grow the hoarfrost, particularly at low and mid slope elevations.
Forecast models continue to suggest a weak wave moving across the
Northern Rockies on Wednesday, however any snow that develops will
produce negligible snow accumulations for much of the region.
Friday night through Sunday morning, a Pacific storm is
anticipated to bring up to a foot of new snow accumulation to much
of the Northern Rockies high elevations. Gusty west and northwest
winds at ridges appear likely during peak snowfall and strongest
near the Continental Divide. Again, is this the beginning of the
next storm cycle? Forecast models are still skeptical.
--Zumpfe
Kootenai:
--------------------------- 5000-7000 FT ----------------------------
Today Tonight Wed
Cloud Cover 60% 70% 55%
Hi/Lo Temps 18 to 28 15 to 23 23 to 32
Winds(mph) W 5 SW 5 S 3
Precip Chc 0 0 0
Precip Type none none snow
Liquid Amt 0.00 0.00 0.00
Snow Ratio(SLR) 0 0 13:1
Snow Amt(in) 0 0 0
Snow Level 500 1000 1000

Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit. For a recorded version of the Avalanche Advisory call (208)765-7323.

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